[196.05] Star Formation in Space and Time: The Orion Nebula Cluster

E. Huff, S. Stahler (UC Berkeley)

We investigate the star formation history of the Orion
Nebula Cluster in both space and time, using the dataset
compiled in Hillenbrand (1997). A previous study (Palla &
Stahler 1999) found that star formation in the region has
accelerated in time, with the bulk of the population forming
within the last few million years. We now demonstrate that
this acceleration occurred simultaneously, and with equal
magnitude, throughout the parent cloud. We find no mass
segregation in the traditional sense; the stars produced
have the same mass distribution everywhere, with the
significant exception of the central Trapezium. In addition,
there appears to be no evidence that low-mass stars tended
to form more recently. The present-day distribution of stars
suggests that the parent cloud, just prior to its
dissipation, is well described as a singular isothermal
sphere. We use a simple, heuristic model to show that clouds
supported by dissipative turbulence undergo accelerating
contraction. Accelerating star formation, observed both in
the Orion Nebula Cluster and elsewhere, should be a natural
consequence of this process.